This invention pertains to novel liquid, foamable acid compositions and to foams prepared from said compositions. This invention also pertains to the use of said foams in cleaning ferrous surfaces and fracturing subterranean formations.
Foams of aqueous acids have been described previously. These acid foams have been used, for example, to clean ferrous surfaces and in fracturing subterranean formations. The acid foams are prepared by frothing a liquid acid comprising a foaming agent (i.e., a surfactant). The foam itself has been typically generated by mechanical means (e.g., mechanical stirrers), by chemical means (e.g., a blowing agent) or by physical means (e.g., bubbling a gas through the liquid). The state of the art is illustrated, for example, by Brenner et al. (U.S. Pat. No. 3,037,887), Crowe et al. (U.S. Pat No. 3,436,262), and Blauer et al. (U.S. Pat. No. 3,937,283). The disclosures of these patents are incorporated herein by reference.
Brenner et al. describe foamable acid compositions, the use of acid foams in cleaning of ferrous surfaces and also describe mechanical methods of generating the foam. The liquid, foamable acid compositions described by Brenner et al. comprised an acid solution containing a foaming or frothing-producing aid. These foaming or frothing aids are substances known to the industry as surfactants which, by decreasing the surface tension of the liquid, render the liquid more readily foamable and produce a more stable foam. These surfactants are cationic, anionic, or nonionic in nature. The foams were produced by blowing a gas through the liquid.
Crowe et al. describe acid foams which are similarly useful in cleaning ferrous surfaces. The liquid, foamable acid compositions described by Crowe et al. were acid solutions comprising a surfactant and a "blowing agent" which was liquid or solid as incorporated into the composition but became a gas at an elevated temperature. The foam was thus produced by heating the composition to the point at which the blowing agent became gaseous.
Blauer et al. described a stable acid foam which was used to fracture subterranean formations. The liquid, foamable composition likewise comprised a surfactant dissolved in the liquid acid (or base), a propping agent (e.g., sand) and a gas.
In each of these utilities, it is desirable that the foam height and stability be increased as much as possible to maximize performance.